It's not the boardrooms of old-fogey Fortune 500 companies that are dominated by dudes!

Sheila Lirio Marcelo took her company Care.com (a platform for finding babysitters and other caregivers) public on Friday. But, as the Wall Street Journal points out, hers is quite a rare story. Between 1996 and 2013, just 3 percent of companies that did an IPO were led by women CEOs. In 2013, 82 companies went public, but only two had female CEOs.

That's according to the research of Martin Kenney (a sociologist) and Donald Patton (an economist) at UC Davis. And there are probably many, many contributing factors at work here. The study excluded "blank-check shell companies, real-estate investment trusts, companies founded more than 30 years ago, and spinoffs of larger companies."

That left a lot of fast-growing companies, many of them in tech, backed by venture capitalists who are (as Kenney pointed out) overwhelmingly men. The WSJ cites a 2011 survey saying women are just 11 percent of investors.

"It's not necessarily that there's some sort of discrimination, but rather structural factors," Kenney told the Journal. But they're not mutually exclusive—the kind of "pattern matching" that assumes a successful CEO will look like either Mark Zuckerberg (for a fast-and-loose startup) or Jack Welch (for anything more buttoned-up) is its own kind of discrimination, even if it's unconscious.